Liquid crystal display (LCD) devices are display devices which control the alignment of birefringent liquid crystal molecules to control the transmission/shielding of light (on/off of display). Examples of display modes of the LCDs include a vertical alignment (VA) mode in which liquid crystal molecules with negative anisotropy of dielectric constant are aligned vertically to a substrate surface; an in-plane switching (IPS) mode and a fringe field switching (FFS) mode, in which liquid crystal molecules with positive or negative anisotropy of dielectric constant are aligned horizontally to a substrate surface and a horizontal electric field is applied to a liquid crystal layer.
Among these modes, a multi-domain vertical alignment (MVA) mode utilizing liquid crystal molecules with negative anisotropy of dielectric constant and alignment-regulating structures (e.g. banks (ribs), hollow portions (slits) of electrodes) is capable of aligning the liquid crystal molecules in multiple directions during voltage application even without rubbing treatment on an alignment film, and is excellent in viewing angle characteristic. In conventional MVA-LCDs, however, upper portions of the ribs or upper portions of the slits serve as the boundaries of alignment division of the liquid crystal molecules, deteriorating the transmissivity during white-image display and causing dark lines in displayed images. Thus, there is room for improvement.
Therefore, alignment-stabilizing techniques using a polymer (hereinafter, also referred to as polymer sustained (PS) techniques) have been suggested as methods of producing LCDs with high luminance and high response speed (for example, see Patent Literatures 1 to 8). In a pre-tilt-angle-imparting technique using a polymer (hereinafter, also referred to as a polymer sustained alignment (PSA) technique) among these PS techniques, a liquid crystal composition containing a polymerizable component such as a polymerizable monomer and oligomer is sealed between the substrates, and the monomer is polymerized with the liquid crystal molecules being tilted (inclined) by a voltage applied between the substrates, thereby forming a polymer. This provides liquid crystal molecules tilted with a predetermined pre-tilt angle even after the voltage application is stopped, and the alignment direction of the liquid crystal molecules is controlled to a certain direction. The monomer is selected from a material polymerizable by heat, light (ultraviolet light). The liquid crystal composition may contain a polymerization initiator for initiating the polymerization of the monomer (for example, see Patent Literature 4).
On the other hand, a photo-alignment technique has been recently studied as a technique for achieving an excellent viewing angle characteristic; this technique is capable of aligning the liquid crystal molecules in multiple directions during voltage application even without rubbing treatment on an alignment film, and is capable of achieving an excellent viewing angle characteristic. The photo-alignment technique is a technique in which an alignment film is formed from a photoactive material and the film is irradiated with light (e.g. ultraviolet light), thereby giving an alignment-regulating force to the alignment film.
Some recent papers disclose that combination use of such a photo-alignment (PA) technique, a rubbing technique, and the aforementioned PS technique for improving the alignment stability in liquid crystal display devices of the IPS mode can provide good results (for example, see Non-Patent Literature 1).